1. Field of the Invention
This invention relates to a film separation method, for separating a film such as a surface protective film attached to the front surface of a wafer, and a film separation apparatus for carrying out the method.
2. Description of the Related Art
In a semiconductor fabrication process, a wafer size has been increased and, to improve the package density, the wafer thickness has been decreased. In order to reduce the thickness of the wafer, a surface protective film is attached on the front surface of a wafer formed with semiconductor devices, and the back surface of the wafer is ground, in what is called a back-grind process, with the wafer surface adsorbed to an adsorption table.
This back-grind process reduces the wafer thickness to, for example, 50 micrometers. Therefore, the mechanical strength of the wafer after the back-grind process is correspondingly reduced. The surface protective film described above must be separated after the back-grind process. According to the prior art, a release tape is attached over the whole of the surface protective film of the wafer, by an application roller, and is rolled off together with the surface protective film thereby to separate the surface protective film. In view of the fact that the mechanical strength of the wafer is greatly reduced, however, a problem is posed that the wafer is often broken when the release tape is attached to the surface protective film.
In order to solve this problem, Japanese Unexamined Patent Publication No. 2004-165570 discloses a method in which the direction of the wafer is adjusted in such a manner that the direction of the release tape fails to coincide with the dicing grooves formed on the wafer. Also, Japanese Unexamined Patent Publication No. 2004-128147 discloses a separation apparatus in which the separation is started from a corner or edge of the wafer.
FIG. 12 is an enlarged sectional view of a wafer, with a surface protective film attached thereon, and indicates that the thickness D0 of the wafer 120 is reduced to D1. As can be understood from FIG. 12, the edge portion 125 of the wafer 120 is chamfered in advance. In order to improve the adhesion by eliminating the gap between the surface protective film 110 and the wafer 120 while at the same time preventing the diameter of the surface protective film from being increased in diameter beyond the wafer size after the back-grind process, what is called an angle-cut process has recently been sometimes executed to cut off the surface protective film 110 in the direction of arrow Z along the chamfered portion of the wafer 120 after the surface protective film 110 is attached.
As shown in FIG. 12, the surface protective film 110, attached on the front surface 121 of the wafer 120 before the back grind process, is configured of a protective film base member 111 and a protective film adhesive layer 112. After executing the angle cut process described above, therefore, the protective film base member 111 of the surface protective film 110 is reduced to a size smaller than the surface 121 of the wafer 120. In such a case, it is difficult to separate the surface protective film 110 in its entirety after the back grind process by simply adjusting or selecting the direction of the wafer 120 or a separation starting point as described in Japanese Unexamined Patent Publication No. 2004-165570 or No. 2004-128147.
Also, the adhesion performance of the release tape changes with the characteristic of the surface protective film constituting an object to be bonded or the specific process executed on the surface protective film after being attached to the wafer. Thus, it may become difficult to attach the release tape to a specific surface protective film or to a surface protective film subjected to a specific process after being attached.
The present invention has been developed in view of this situation, and the object thereof is to provide a film separation method, and a film separation apparatus for carrying out the method, in which even in the case where the surface protective film is cut off along the chamfered portion of the wafer or in the case of a specific surface protective film or a surface protective film subjected to a specific process, the release tape can be easily integrated with the surface protective film and easily separated together with the surface protective film.